The present invention relates to an AC power control circuit for use with various types of loads.
As energy costs increase and the use of electric lighting and motors expands, more and more attention is being given to the design of efficient electrical systems. SCR (Silicon Controlled Rectifier) and Triac based AC (alternating current) voltage controllers have long been in use for controlling resistive loads (i.e. loads in which there is no phase difference between the voltage and the current). There are also systems which have been proposed for controlling the AC power supply to non-resistive loads such as fluorescent lights. For example, U.S. Pat. No. 4,287,455 issued Sep. 1, 1981 to M. L. Drieu, discloses a control circuit which supplies current to one or more gaseous discharge lamps during an adjustable final portion of each half-cycle of the AC power supply. However, since this circuitry allows current to pass through the load only during the final portion of each half-cycle of the AC power supply, an inductive effect is produced, i.e. a time lag is created between the peak line voltage and the peak line current. This inductive effect affects the power factor. Since utility companies generally charge commercial users a higher rate if the power factor falls below a particular value (e.g. 90), the reduction in power occasioned by the use of some prior art power saving circuits may in some cases be offset by the higher rate charged by the utility company.
Prior art power saving circuits have been devised that control the AC power supplied to a load by using a form of reverse phase control whereby current flow begins at the beginning of an AC half-cycle but is terminated before the end of the half-cycle. By determining the point at which current flow is stopped, reverse phase control circuits can produce a capacitive effect. Circuits that employ reverse phase control have been disclosed in U.S. Pat No. 5,455,491 issued Oct. 3, 1995. However, the circuits disclosed in these patents do not function as well as might be hoped when used to control power supplied to fluorescent lights because the extended period of zero current near the end of each half-cycle can result de-ionization occurring in some fluorescent lamps. Additionally, these reverse phase control systems lack the flexibility to produce an inductive effect so that they can also be used to improve the power factor when used with a capacitive load.
Also, it is desirable to provide a simplified power control circuitry which allows control of very high power but which consumes very low amounts of power, and which can satisfactorily reduce power consumption while at the same time allowing for power factor control when used with an inductive, capacitive or resistive load.
The present invention provides a power control circuit for connection to an AC supply circuit for supplying current to a load. The power control circuit reduces power consumption while drawing very low power itself
According to one aspect of the invention, there is provided a power control circuit for connection to an AC supply circuit for supplying AC current to a load, comprising a bilateral, very high speed power control switch for connection in series with the load, a bilateral, very high speed energy return switch for connection in parallel with the load, and a driver circuit connected to each of the power control switch and the energy return switch for controlling the opening and closing of the switches. The driver circuit is configured to cause the energy return switch to be open when the power control switch is closed and the energy return switch to close when the power control switch opens. A timer circuit is operatively connected to the driver circuit for controlling the operation of the driver circuit so that the power control switch is closed for at least a predetermined initial time period and a discrete predetermined final time period during each half cycle of the AC current. The power control circuit also includes a power supply circuit for connection to the AC supply circuit for supplying power to the driver circuit and timer circuit.
According to another aspect of the invention, there is provided a power control circuit for connection to an AC supply circuit for supplying AC current to a load, comprising a bilateral power control switch for connection in series with the load, a bilateral energy return switch for connection in parallel with the load, and a driver circuit connected to each of the power control switch and the energy return switch for controlling the opening and closing of the switches, the driver circuit being configured to cause the energy return switch to be open when the power control switch is closed and the energy return switch to close when the power control switch opens. The power control circuit also includes a timer circuit operatively connected to the driver circuit for controlling the operation of the driver circuit so that the power control switch is successively closed and opened at least once during each half cycle of the AC current, and a power supply circuit for connection to the AC supply circuit for supplying power to the driver circuit and the timer circuit, the power supply circuit being a low power consumption circuit that includes a low power resistor means for connection in series with the AC supply circuit for reducing an AC line voltage to a voltage level suitable for application to the driver circuit and the timer circuit.
According to still a further aspect of the invention, there is provided a power control circuit for connection to an AC supply circuit for supplying AC current to a load, comprising, a bilateral power control switch for connection in series with the load, a bilateral energy return switch for connection in parallel with the load, and a driver circuit connected to each of the power control switch and the energy return switch for controlling the opening and closing of the switches, the driver circuit being configured to cause the energy return switch to be open when the power control switch is closed and the energy return switch to close when the power control switch opens. A timer circuit is operatively connected to the driver circuit for controlling the operation of the driver circuit so that said power control switch is successively closed and opened at least once during each half cycle of the AC current. The power control circuit also includes a power supply circuit for connection to the AC supply circuit for supplying power to the driver circuit and the timer circuit, and a high power, transient suppressor circuit including a bilateral suppressor for connection across the AC supply circuit and monitoring means operatively connected to the bilateral suppressor for monitoring the potential across the AC supply circuit and causing the bilateral suppressor to close when the potential exceeds a predetermined value.